Why Hydroelectricity from Large Dams is Not Clean

It’s common, if not the rule, for hydroelectricity from dams to be listed as clean energy. With approximately 845,000 dams worldwide (~80,000 in the US) it seems like people have for a long time believed this to be true, and you can’t really blame them. Dam building is often a very political issue and politicians often lead people to believe this myth. Besides that, without knowing all of the facts it would seem like they are clean; you have a river, you put up a dam and send then water through tunnels that turn turbines and out comes electricity, from water! But once you look at all of the details you will see that there are a number of reasons why hydroelectricity from dams is in fact not clean at all.

So why isn’t hydroelectricity from dams clean? Here are a few of the reasons:

Let’s talk about one of the main materials that go into a dam: concrete. First, to give you an idea of how much concrete goes into a dam and its associated infrastructure I’ll tell you that the Hoover Dam is made up of 4,360,000 cubic yards of concrete. While that number is too big to really understand you and I know that it’s a lot of concrete. To make that concrete you need cement, and that requires the mining of limestone, and mining is a dirty job that is known to have negative impacts on the surrounding environment and water. Once it’s mined the limestone is transported in big trucks (that produce CO2) to a cement plant where it is heated (by coal-fired kilns). When it is heated the limestone itself produces CO2. All this CO2 and we’ve only talked about one ingredient in concrete. You also have to take into account the mining and transportation of aggregates and sand that go into the concrete. Further, you need water to make all this work. Typically about 25% of a concrete mix is water, and that water needs to be taken from somewhere.

When the area behind a dam is flooded all of the vegetation in this new reservoir

Photo via internationalrivers.org

dies. As the tree’s and vegetation rots and decays it gives off CO2. That’s bad. But wait, there’s more. They also give off methane! Methane is worse than CO2 because it is more efficient in trapping heat. This all happens because when the trees and plants die the organic carbon in plants is converted into methane and CO2 which is then released into the atmosphere. And this doesn’t just happen when the reservoir is initially filled. When the level of the reservoir drops new plants can start growing along the edges. Once it raises again the plants die and the cycle continues. Some people even say that dams can produce more greenhouse gases then power plants running on fossil fuels. If you want to read more about this just do a quick google search and you’ll find a lot of information.

Let’s talk water now. There are a few ways that dams impact water.

The composition of water is drastically changed when stored in a reservoir. Because the water is just sitting there in a large pool it evaporates quicker than if it was a naturally flowing river. This evaporation leads to the water becoming more saline because the salt in the water becomes more concentrated. The source of the salt is usually soil. When it rains or water is used for irrigation is runs through the soil and picks up salts and then flows down to a river or creek. Some water can be re-used for irrigation 15+ times, and each time it’s picking up more salts. High salinity of water makes it unusable and toxic to humans, animals, plants, and the machinery in the dam.

Being stored behind a dam also changes the temperature of the water. When you change the natural temperature of river water it affects the amount of dissolved oxygen (lowers it) and suspended solids. Healthy river water has an adequate amount of dissolved oxygen in it which makes it safe to drink. When you lower the amount of dissolved oxygen you can essentially suffocate aquatic organisms, and impede the ability of bacteria to break down pollution in the water, leaving it unfit to drink (and you’re killing all the little organisms).

Dams also keep nutrients in the water from flowing downstream, and trap them in the reservoir. This can lead to large algae plumes on the surface of the reservoir which can keep light that organisms need to survive from penetrating the surface as well as eating up oxygen that fish and other organisms need to survive.

Another problem that has only recently come to light is high levels of mercury in the reservoirs. Mercury is naturally occurring in harmless inorganic forms in the soil. However, when a reservoir is first flooded the bacteria that are feeding on the decomposing plants turn the harmless mercury into methylmercury, a central nervous system toxin. The methylmercury is absorbed by plankton and other organisms at the bottom of the food chain. As the food chain works and these organisms are eaten, and then those are eaten, etc. the concentration raises. When you get to the large fish in the reservoir you can see levels of methylmercury several times what they started as in the original organism. This leaves the fish inedible, and that’s a problem for people that depend on the fish as a food source.

Anyone who follows my facebook page (facebook.com/hydratelife) will have noticed that I put up a lot of articles about dams. From the Gibb III in Kenya to the Belo Monte in Brazil to the Xayaburi in Laos, people are fighting every day against dams, and for their livelihood. Besides everything I wrote about above dams are extremely destructive to the surrounding environment and its people. Communities are displaced by the construction and the reservoir waters, because the water downstream of the dam that they depend on dries up, and/or because the fish they depend on are no longer there. They can also be impacted if they use the water for agriculture, either because they now have no water, or because the water is no longer any good to grow crops. Any way you cut it dams are a detriment to the environment and the people around the dam site.

Now, so that I don’t have people yelling at me let me take a minute to say that I understand a lot of people have electricity solely because of dams. That’s great and I’m sure they’re very happy when they get home and can turn on a light. The argument of this article is to point out that while dams do create electricity there are a number of different ways that the same electricity can be produced in a way that is truly clean (wind and solar just to name a few obvious ones), and we need to start using those instead. I’ve written about a few other options that I thought were really interesting: bioWave, The Free Flow Kinetic Hydropower System.

So why aren’t these other options used? I can’t really say for sure, but I once read or saw a video where someone was talking about dams, and they said that countries just keep building dams because the dam companies are there, and dam companies build dams. These huge dam construction companies have a lot of power (and money) to persuade governments, and so governments don’t look for other options. I thought that was an interesting observation, and that may very well be the reason we keep building dams. Thanks for reading.